Leave it to Dave Grohl, rock’s great ambassador, to bring together everyone from Joe Perry to Rick Astley for one giant cranked-to-11 party in the sweltering Inland Empire. “Someone said, ‘Hey, you wanna have a record release party somewhere?’” explained Grohl, whose Foo Fighters just released their chart-topping ninth studio album, Concrete and Gold. “I said OK. They said, ‘What about the Hollywood Bowl?’ I said, ‘You know what? Nah. That s*** ain’t loud enough!’”

But of course, when a rock star invites “all his friends” to a wild all-day party, at least one of those guests is going to be a troublemaker. And that role Saturday was amusingly filled by ex-Oasis mouthpiece Liam Gallagher, promoting his debut solo album, As You Were. Teaming with Perry (whose Aerosmith had performed at Cal Jam II in 1978) and the Foos for an utterly bizarre, if highly entertaining, ramshackle cover of the Beatles’ “Come Together,” nothing really came together during his performance. But it was fascinating to behold. And it was totally rock ‘n’ roll.

The song choice made sense — Aerosmith’s charismatic “Come Together” scene was the highlight of the 1978 Sgt. Pepper box-office bomb, and the younger Gallagher brother’s Beatles fixation is of course well known. But this “Come Together” was almost weirder than the movie version.

When Gallagher shuffled out in a parka and baggy shorts, he immediately bungled all of the tune’s (admittedly tricky) wordplay, and even when he was handed a poster-sized lyric sheet, he still managed to get about half the words wrong. He then summoned a woman to the stage to sing a few lines — and while her amateur vocals weren’t impressive, she did seem more familiar with the lyrics than Gallagher.

The surly Britpop icon then leapt into the crowd, trailed by panicked security guards, for an awkward crowd-surf attempt, while the supergroup soldiered on behind him and the random onstage fan danced.

Earlier in the Foos’ set, Perry played a fiery “Draw the Line,” a song from Aerosmith’s Cal Jam II setlist; Rick Astley Rickrolled the show with a grungy reprise of “Never Gonna Give You Up” (which the Foos and Astley originally performed at August’s Tokyo Music Festival); and the Kills’ Alison Mosshart and smooth jazz saxophonist Dave Koz joined in for the Concrete and Gold cut “La Dee Da.” All of these collaborations went much more smoothly — but Gallagher’s crazy cameo was understandably the talk of the night. (Warning: Some videos below contain strong language.)

Cal Jam had its share of more somber moments. Bob Mould opened his show with a speech about his late Hüsker Dü bandmate Grant Hart and a dedication of that group’s classic “Never Talking to You Again.” Cage the Elephant opened their set with “Mary Jane’s Last Dance” (which they performed at MusiCares’ Person of the Year gala honoring Tom Petty during this year’s Grammy week), and Starcrawler played their own garage version of that 1993 Heartbreakers hit. Grohl also dedicated the Foo Fighters’ “Hero” to Petty, while standing in front of a drum kit printed with a vintage photo of another rock legend we lost this year, Chris Cornell.

QOTSA’s Josh Homme, who had attended Petty’s final show at the Hollywood Bowl on Sept. 25 with his dear friend Grohl, also addressed the previous weekend’s horrific festival tragedy. Spotting an audience member’s homemade sign that read “VEGAS STRONG,” with the 58 names of the Route 91 Harvest festival’s shooting victims written on the back, Homme took the sign, held it aloft, and declared amid massive cheers: “We are everything when we are together. Let’s have the f***ing time of our lives.”

It was a sweet reminder of the power of music — and music festivals — to unite and help people forget their troubles, if only for one sunny day. Come together, indeed.